Pull type friction clutches for medium and heavy duty trucks commonly have a retainer sleeve disposed over a transmission input shaft. The sleeve connects a release bearing with a retainer. The release bearing has an outer portion engaged by the clutch release linkage. The retainer is engaged by clutch levers, or the tips of radially inwardly extending diaphragm spring fingers. The retainer, retainer sleeve and release bearing are all selectively displaced in an axial direction along the input shaft to engage and disengage the clutch.
The retainer, the retainer sleeve and an inner bearing race of the release bearing rotate as a unit with a pressure plate and a cover of the clutch. The outer race of the release bearing does not rotate relative to a transmission housing because it is engaged to a clutch yoke. The clutch yoke comprises part of the clutch actuation linkage. The clutch pressure plate and cover are rotatively fixed to an engine flywheel and rotate as a unit therewith.
A clutch driven disc is rotatably connected with the transmission input shaft for rotation therewith. When the clutch is engaged, the driven disc and the input shaft rotate at the same speed as the engine flywheel. When the clutch is disengaged, the driven disc and input shaft are uncoupled from those parts of the clutch which rotate with the engine, permitting relative rotation between the input shaft and the retainer sleeve. Differential speed between the retainer sleeve and the input shaft contributes to the wear of the retainer sleeve. Anti-friction bushings are commonly disposed in the retainer sleeve to help reduce the consequences of the engagement between the input shaft and the sleeve. However, grooves cut into the input shaft form edges which can damage the bushings. Also, customer expectations of increasingly longer periods of service free operation require further improvement of the retainer sleeve to input shaft interface.
Clutch brakes are used in heavy duty and medium duty trucks to slow a transmission input shaft, and therefore the gears within the transmission, to facilitate shifting of a non-synchronized manual transmission. A clutch brake is slidably disposed on the input shaft between the release bearing and the transmission housing. The clutch brake is engaged by using the clutch linkage to pull the release bearing back to the full extent of its travel, compressing the clutch brake between the release bearing and the transmission housing or a feature rotatably fixed to the housing. One type of clutch brake has its engagement surfaces rotatably fixed to the input shaft. This is an inexpensive configuration because a one piece brake can be employed. Friction elements fixed to a hub are used to provide the engagement surfaces. However, such brakes absorb a high level of energy wearing the friction element and require servicing at a higher than desired frequency. Another type of clutch brake is a torque limiting clutch brake. Torque limiting clutch brakes allow slippage to occur internally between a first portion rotatably fixed to the input shaft and a second portion axially engaged by the release bearing and the transmission housing. The slippage increases the life of the brake by reducing the rate at which the brake must absorb energy. However, because they comprise a number of components including springs, a hub portion and an outer shell that must be assembled, such torque limiting brakes are more expensive than a non-slipping brake. Additionally, to service known torque limiting clutch brakes, the transmission must be separated from the engine. This is a very time consuming and therefore expensive service operation.